We propose to continue investigations of the biosynthesis and biological function of ferritin protein made on the rough endoplasmic reticulum of cell such as rat hepatocytes or rat hepatoma cells. We also propose to continue investigations of isoferritin protein synthesis by rat hepatocytes and Kupffer cells in vitro, and we propose to begin investigations of the relation of ferritin protein synthesis by intestinal epithelial cells to states of iron overload and of iron deficiency in isolated loops of intestine, in vivo and in vitro. In these investigations biochemical and immunochemical methods will be used in conjunction with electron microscopy.